Abstract

The heavy ion program developed at the CERN SPS since 1986 has given an impressive set of results. It has been successful in delivering precise data on the production of the quark-gluon plasma. Signatures of the formation of this new state of matter in heavy ion collisions have been proposed. Among the most exciting observations are screening effects, thermal radiations, multi-strange enhancement, chemical equilibrium and strong collective effects. This article gives a short review of these data and of our understanding of the underlying physics. The analysis of the data provided by seven large experiments indicates that the transition from the deconfined phase to ordinary hadronic matter coincides with the critical lattice QCD temperature (≈170 MeV) corresponding to a critical energy density ≈1 GeV/fm3.